fix(dcp): correct storage path to match OpenCode's actual location

DCP was failing to find session messages because it was looking in
~/.config/opencode/sessions instead of ~/.local/share/opencode/storage.
Unified all hooks to use getOpenCodeStorageDir() for cross-platform consistency.

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/agent-usage-reminder/constants.ts

@@ -1,7 +1,7 @@
 import { join } from "node:path";
-import { xdgData } from "xdg-basedir";
+import { getOpenCodeStorageDir } from "../../shared/data-path";
 
-export const OPENCODE_STORAGE = join(xdgData ?? "", "opencode", "storage");
+export const OPENCODE_STORAGE = getOpenCodeStorageDir();
 export const AGENT_USAGE_REMINDER_STORAGE = join(
   OPENCODE_STORAGE,
   "agent-usage-reminder",